72
E. NAYLOR
equilibrium between the competing barnacles Ch+thamlus stellatus (Poli)
and Balanus balanoides in Britain. Such changes, if sufficiently prolonged, cause the boundaries of distribution of each species to alter considerably, so that slight increases in temperature result in a northward
spread of the low latitude species, Chthamalus, at the expense of the
high latitude species, Balanus, and vice versa. As Southward (1958)
points out, the evidence for a causal relation between temperature
and distribution in this way must be sought in non-lethal terms such as
debilitating effects, or indirectly through competition, or in combination
with other factors.
Finally, if electricity generating stations tended to produce more
power in winter and consequently discharge greater quantities of heat
at that time, their effluents would result in a narrowing of the annual
range of temperatures in the discharge area. Extensive narrowing of
the seasonal range of temperature would probably have considerable
biological effects since it is known that a constant temperature of a
particular value and fluctuating temperatures of that average value do
not necessarily have the same biological effects (Kinne, 1963). For
instance, the brackish-water amphipod Gammaiwus duebeni exhibits
normal growth rates, reproduction rates, sex ratio and life span only
under conditions simulating annual fluctuations in the environment
(Kinne, 1952, 1953a,b,c).
D. Behaviour
Many inshore marine species and estuarine forms undertake migrations to deeper water in winter. Such migrations are well documented
in Crustacea (Bainbridge, 1961; Naylor, 1962; Kinne, 1963) where
salinity and temperature are controlling factors. Temperature changes,
too, govern the seawards and riverwards migrations of salmon (Foerster,
1937), which in rivers are sometimes killed by heat during hot summers
(Huntsman, 1942). I n considering the biological effects of siting heated
effluents in estuaries the possible long-term effects upon migratory
species should, therefore, not be overlooked.
E. Acclimatization*
Despite the sensitivity of many species to high temperatures there
is nevertheless accumulating evidence that many poikilothermic
* The term "acclimation" is avoided here. It is sometimes used to indicata
experimentally induced and fairly rapid thermal adaptation, aa distinct from slow,
naturally occurring adaptation (see Erichsen Jones, 1964). Other authors, on the other
hand, still use " eccliimation " synonymouely with the term " acclimatization " w
ueed here (see Kinne, 1963).
E. NAYLOR
equilibrium between the competing barnacles Ch+thamlus stellatus (Poli)
and Balanus balanoides in Britain. Such changes, if sufficiently prolonged, cause the boundaries of distribution of each species to alter considerably, so that slight increases in temperature result in a northward
spread of the low latitude species, Chthamalus, at the expense of the
high latitude species, Balanus, and vice versa. As Southward (1958)
points out, the evidence for a causal relation between temperature
and distribution in this way must be sought in non-lethal terms such as
debilitating effects, or indirectly through competition, or in combination
with other factors.
Finally, if electricity generating stations tended to produce more
power in winter and consequently discharge greater quantities of heat
at that time, their effluents would result in a narrowing of the annual
range of temperatures in the discharge area. Extensive narrowing of
the seasonal range of temperature would probably have considerable
biological effects since it is known that a constant temperature of a
particular value and fluctuating temperatures of that average value do
not necessarily have the same biological effects (Kinne, 1963). For
instance, the brackish-water amphipod Gammaiwus duebeni exhibits
normal growth rates, reproduction rates, sex ratio and life span only
under conditions simulating annual fluctuations in the environment
(Kinne, 1952, 1953a,b,c).
D. Behaviour
Many inshore marine species and estuarine forms undertake migrations to deeper water in winter. Such migrations are well documented
in Crustacea (Bainbridge, 1961; Naylor, 1962; Kinne, 1963) where
salinity and temperature are controlling factors. Temperature changes,
too, govern the seawards and riverwards migrations of salmon (Foerster,
1937), which in rivers are sometimes killed by heat during hot summers
(Huntsman, 1942). I n considering the biological effects of siting heated
effluents in estuaries the possible long-term effects upon migratory
species should, therefore, not be overlooked.
E. Acclimatization*
Despite the sensitivity of many species to high temperatures there
is nevertheless accumulating evidence that many poikilothermic
* The term "acclimation" is avoided here. It is sometimes used to indicata
experimentally induced and fairly rapid thermal adaptation, aa distinct from slow,
naturally occurring adaptation (see Erichsen Jones, 1964). Other authors, on the other
hand, still use " eccliimation " synonymouely with the term " acclimatization " w
ueed here (see Kinne, 1963).